But when NBC News traced a particular brand of jerky treat from the shelves of U.S. stores all the way back to a specific factory in Shandong, China, that manufactured treats for a variety of U.S. companies, the owner of the factory did not hesitate to pop a pet treat into his own mouth.

“It’s safe, no problem,” said Luke Qin, and demonstrated by wolfing down a duck jerky treat. “Human standard. You can try eating.”

But Qin also said his business had suffered, and he had to close four of his five factories had to shut down, after U.S. consumers and pet food manufacturers began to shy away from Chinese-sourced jerky after reports of pet illnesses.

For seven years, the FDA has been investigating possible links between Chinese jerky pet treats and maladies in dogs that include gastrointestinal illness, kidney failure and a disease called Fanconi syndrome. Its most recent report tabulated nearly 5,000 alleged cases of jerky-linked illness.

Brooklyn, N.Y., veterinarian Brett Levitzke said he has seen a dozen fatalities since 2011. “There’s definitely something in those treats that cause these signs and this syndrome,” said Levitzke. He said that in the absence of any other explanation he had “no doubt” of a link between the illnesses and the treats.

More than a year ago, U.S pet food companies began pulling dog treats using Chinese chicken from their shelves after finding residues of antibiotics. In January 2013, Hartz Mountain, Del Monte and Nestle Purina pulled chicken jerky treats made in China from the market after illegal antibiotics were found in their products. The FDA said it did not believe the low levels of antibiotics found had caused illnesses.

In November 2013, NBC News used the Panjiva on-line database to review Customs records and trace a shipment of one of the pulled products, Nestle Purina’s Waggin’ Train chicken treats, to Qin’s factory in China.

At the factory, NBC News found a package of Del Monte’s Milo’s Kitchen chicken jerky treats, another of the products that had been pulled from shelves. Qin confirmed that he had supplied chicken jerky treats to both Del Monte and Nestle Purina, but said he no longer did.

“I used to be the biggest supplier [to the U.S.],” said Qin.

Qin said he was still exporting products to the U.S., but at lower volumes. A package of Cadet Gourmet Duck Breast jerky treats, a product marketed by IMS Pet Industries of Wood-Ridge, N.J., was coming off the assembly line as he spoke. He ate one of the treats to underline his contention that his products were safe.

The FDA has visited Qin’s Shandong factory and given it a clean bill of health, though Chinese regulators would not let them take samples out of the country for testing.

In the most recent FDA report, the humans who were reported to have been sickened after eating the products included two toddlers who ate them accidentally and an adult who may have been snacking on them on purpose.

One child was diagnosed with salmonella, another developed a gastrointestinal illness similar to that of the dogs sickened by the treats, and the adult reported nausea and headache, according to an FDA spokesperson.

But in seven years of testing, the FDA has never identified a specific cause for the reported illnesses, though it continues to warn pet owners about the products. It has now asked the Centers for Disease Control for help in identifying a cause.

Meanwhile, U.S. manufacturers, who say their products are safe, have begun putting the pulled products back on the shelves-- though they have started sourcing some products in the U.S. In February, Nestle Purina Pet Care reintroduced a line of Waggin’ Train treats for dogs, including products made from a single supplier in China and new products sourced entirely in the U.S. Del Monte’s Milo’s Kitchen has also returned to shelves using U.S.-sourced meat.

“We've listened to our consumers,” said Del Monte in a statement, “and made a decision not to source even minor ingredients from China, as of April 2014.”

Nestle Purina and IMS did not immediately respond to requests for comment.

Ian Williams

Ian Williams is a former NBC News correspondent and the author of "Beijing Smog," a satirical novel about modern China and the power of online ridicule.

Originally from Liverpool in the U.K., Williams also has worked for the British broadcaster ITN, where he worked as Channel 4 News' Moscow correspondent and Asia correspondent based in Hong Kong and Bangkok. He previously was a business correspondent for London's Sunday Times newspaper.

Monica Alba

Monica Alba is a White House producer for NBC News.

JoNel Aleccia

JoNel Aleccia is a contributing writer for the Food & Environment Reporting Network. She was a senior health reporter and editor for NBC News for six years.

Aleccia is the co-recipient of two Joan M. Friedenberg Online Journalism Awards, in 2009 and 2011, from the National Press Club. She also has received multiple regional and local journalism awards.

Tom Winter

Tom Winter is a producer and reporter for the NBC News Investigative Unit based in New York, covering crime, courts, terrorism, and financial fraud on the East Coast.